The results were published as part of an operation dubbed "In Our Sites" (IOS), a global effort launched in 2014 which draws on expertise from 27 EU member states and is spearheaded by Europol's Intellectual Property Crime Coordinated Coalition (IPC³).

On Monday (27 November) Europol said that a total of 7,776 websites had been seized in previous swoops while this year's operation, codenamed IOS VIII, resulted in 20,520 seized domain names being scrubbed from the web after they were caught illegally selling counterfeit merchandise.

Rob Wainwright, director of Europol, said: "This excellent result shows how important and effective cooperation between law enforcement authorities and private-sector partners is, and how vital it is if we are to ultimately make the internet a safer place for consumers."

The European police agency said that counterfeiters running rogue websites were becoming more sophisticated and warned that the web continued to offer criminals increased anonymity.

On its website, Europol elaborated: "When shopping online, you are more likely to fall victim to counterfeiters. In a digital environment, without the physical product to look at and feel, it can be more difficult for you to spot the differences.

"Some illicit websites selling counterfeits are so sophisticated that it is hard to detect that they are scams. Infringers are also exploiting mobile app stores as an ideal shop front. Users are less likely to question the legitimacy of an app, especially if it appears in an official app store."

Nick Annan, acting director of the National Intellectual Property Rights Centre, said: "Targeting copyright-infringing websites that market dangerous counterfeit goods to consumers and engage in other forms of intellectual property theft will continue to be a priority.

"Strengthening our collaboration with police authorities around the world and leaders of industry will reinforce the crackdown on IP crimes, and demonstrate that there is no safe haven for criminals committing these illicit activities."

According to Europol, some of the most popular counterfeit goods sold online includes fake designer watches, dodgy electronics, cosmetics, clothing, drugs, children's toys and car parts. "You will receive product other than the one you ordered or even an empty box," it warned.